1. Field of the Invention
The present invention relates to an article transport facility and more particularly to an article transport facility comprising two or more article processing devices installed on the ground side and an article transferring point provided on the ground side in association with each of the article processing devices, a plurality of article transport vehicles that transport articles among the article processing devices, and travel paths which are installed on the ceiling side and in which the plurality of article transport vehicles travel.
2. Description of the Related Art
In article transport facilities such as one described above, because a travel path along which an article transport vehicle travels is installed on the ceiling side or to the ceiling and because article processing devices and the article transferring points for the article processing devices are installed on the ground, the article transport vehicle is provided with a grip portion for gripping an article such that the gripping portion can be moved vertically. Thus, an article transport vehicle travels along the travel path to a stop position that is associated with an article transferring point and transfers an article to or from the article transferring point for the article processing device by vertically moving, i.e. by raising and lowering the grip portion. (See, for example, JP Application Publication No. 2006-319154).
In the facility described in the JP No. 2006-319154 above, the travel path includes a plurality of intra-process looped tracks that extend along or by way of a plurality of article transferring points in plan view, and an inter-process looped track that is connected with the plurality of intra-process looped tracks to allow the article transport vehicles to travel between the intra-process looped tracks. Two or more intra-process looped tracks are arranged next to each other in the lateral direction of the path. And each of the intra-process looped tracks and the inter-process looped track consists of a pair of straight portions which face or oppose each other and curved portions which connect the straight portions. Thus, between two intra-process looped tracks which are located next to each other in the path lateral direction of the intra-process looped tracks, a plurality of article processing devices provided in association with one of the intra-process looped tracks are arranged next to each other along its path longitudinal direction and a plurality of article processing devices provided in association with the other of the intra-process looped tracks are arranged next to each other along its path longitudinal direction. Therefore, for the intra-process looped tracks that are located next to each other in the path lateral direction, a straight portion in one of the intra-process looped tracks is a first travel path portion, and a straight portion in the other of the intra-process looped tracks is a second travel path portion.
In JP No. 2006-319154 described above, the transporting efficiency is improved by providing two or more article transport vehicles and by transporting a plurality of articles by the two or more article transport vehicles. However, for example, when an article is transported from the article processing device provided in association with the first travel path portion to an article processing device provided in association with the second travel path portion, the article transport vehicle must travel first on the first travel path portion which is the straight portion in the intra-process looped track, then on the inter-process looped track, and on the second travel path portion which is the straight portion in the intra-process looped track in that order. And it takes a long time to transport the article because of the long distance traveled by the article transport vehicle. In addition, when the article transport vehicle travels on the first travel path portion, an inter-process looped track, and the second travel path portion in order, other article transport vehicles may get in the way, which makes it difficult to travel smoothly. This may also increase the time required to transport an article between an article processing device provided in association with the first travel path portion and an article processing device provided in association with the second travel path portion, thus further reducing the transport efficiency.
To this end, if articles are transported from the article processing device provided in association with the first travel path portion to an article processing device provided in association with the second travel path portion, for example, by providing an inter-travel-paths transport device such as a conveyor for transporting articles between the first travel path portion and the second travel path portion, this inter-travel-paths transport device may be used to shorten the time required to transport articles. However, it is difficult to secure the installation space for such an inter-travel-paths transport device because a number of article processing devices are installed and arranged on the ground along the path longitudinal direction between the first travel path portion and the second travel path portion. That is, a plurality of article processing devices are installed and arranged along the path longitudinal direction between the first travel path portion and the second travel path portion with minimum distances in the path longitudinal direction between article processing devices in order to have as many article processing devices as possible in that space. Therefore, the space for installing an inter-travel-paths transport device can not be secured between the plurality of article processing devices arranged along the path longitudinal direction; thus, the space for installing the inter-travel-paths transport device is limited to the space above the article processing devices.
We note that the article transport vehicle transfers an article to or from a transfer target, such as an article transferring point, by vertically moving the grip portion for gripping an article. Therefore, when an article transport vehicle transfers an article to or from an inter-travel-paths transport device, a sufficient space is required to lower the article gripped by the grip portion to a level lower than the article transport vehicle. Thus, the inter-travel-paths transport device has to be installed at a height that is that much lower than otherwise. As the result, even if an attempt were made to install an inter-travel-paths transport device in the space above the article processing devices, the inter-travel-paths transport device would interfere with an article processing device, thus making it impossible to install an inter-travel-paths transport device in the space above the article processing devices.